Re: battery: current a factor of 10 off?

[Alexey Starikovskiy <aystarik@gmail.com>]

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Hi Ferenc,
This patch should be better -- no integer overflow.

Regards,
Alex.

Alexey Starikovskiy wrote:
> Hi Ferenc,
>
> Good catch.
> ACPI battery interface report its state either in mW or in mA, and
> discharge rate
> in your case is reported in mW. power_supply interface does not have
> such a parameter,
> so current_now parameter is used for all cases. But in case of mW,
> reported discharge should
> be converted into mA.
>
> Please test the attached patch.
>
> Thanks,
> Alex.
>
> On Fri, Nov 21, 2008 at 3:33 AM, Ferenc Wagner <wferi@niif.hu> wrote:
>   
>> Hi,
>>
>> on my ThinkPad R50e the current_now reading seems something like 10
>> times the actual value.  Documentation/power/power_supply_class.txt
>> says it's in uA, and a tipical discharge value is around 15259000,
>> that is, 15 A on my system.  At the same time voltage is 11756000,
>> that is, 12 V, which sounds reasonable, but then the power is 15*12 VA,
>> ie 180 W, which is insane.  However, the numerical derivative of
>> energy_now gives 18 W, which is both reasonable and consistent with
>> the assumed factor of 10 error in current_now.  Is this possibly a bug
>> in 2.6.26.6?  During a quick glance over battery.c nothing obvious
>> jumped at me, but I'm no expert on this.
>> --
>> Thanks,
>> Feri.
>> --
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>>     


[-- Attachment #2: convert_discharge_energy_to_current.patch --]
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ACPI:battery: Convert discharge energy rate to current properly

From: Alexey Starikovskiy <astarikovskiy@suse.de>

ACPI battery interface reports its state either in mW or in mA, and 
discharge rate in your case is reported in mW. power_supply interface 
does not have such a parameter, so current_now parameter is used 
for all cases. But in case of mW, reported discharge should
be converted into mA.

Signed-off-by: Alexey Starikovskiy <astarikovskiy@suse.de>
---

 drivers/acpi/battery.c |    9 +++++++++
 1 files changed, 9 insertions(+), 0 deletions(-)


diff --git a/drivers/acpi/battery.c b/drivers/acpi/battery.c
index 1423b0c..0ebc04c 100644
--- a/drivers/acpi/battery.c
+++ b/drivers/acpi/battery.c
@@ -174,6 +174,15 @@ static int acpi_battery_get_property(struct power_supply *psy,
 		break;
 	case POWER_SUPPLY_PROP_CURRENT_NOW:
 		val->intval = battery->current_now * 1000;
+		/* if power units are mW, convert to mA by 
+		   dividing by current voltage (mV/1000) */
+		if (!battery->power_unit) { 
+			if (battery->voltage_now) {
+				val->intval /= battery->voltage_now;
+				val->intval *= 1000;
+			} else 
+				val->intval = -1;
+		}
 		break;
 	case POWER_SUPPLY_PROP_CHARGE_FULL_DESIGN:
 	case POWER_SUPPLY_PROP_ENERGY_FULL_DESIGN: